Conventionally, in heat transport devices for circulating liquids such as water and alcohol and various other devices involving transfer of liquids, pump devices for pumping liquids by rotation of impellers are widely used. For example, Patent Literature 1 discloses a pump device 100 for use in a pumped storage power plant, as shown in FIG. 10.
This pump device 100 includes an impeller 120 and a suction pipe 110 that forms an inlet passage for introducing water into this impeller 120. A nozzle 130 for injecting high-pressure water toward the impeller 120 is disposed in the inlet passage, and a feed pipe 140 penetrating the inlet pipe 110 is connected to the nozzle 130. In the pump device 100 for use in a pumped storage power plant, cavitation develops as the pump head (pumping height) increases. The nozzle 130 is designed to improve this problem.
In one embodiment of Patent Literature 1, the opening direction of the nozzle 130 is parallel to the axis of rotation of the impeller 120, as shown in FIG. 11A. When the pump head increases, the flow rate decreases and the water inlet angle β into the impeller 120 becomes smaller than the blade angle β0 of the impeller 120, as shown in FIG. 11B. So, high-pressure water is injected from the nozzle 130 to increase the meridional water flow velocity from V to V′. In FIG. 11B, U is the blade rotational velocity, and W and W′ are the relative water inlet velocities into the impeller 120. As a result, the water inlet angle changes from β to β′ and approaches the blade angle β0. Thus, cavitation is unlikely to be generated.
In another embodiment of Patent Literature 1, the nozzle 130 is configured to swing in the rotational direction of the impeller 120 and in the opposite direction with respect to the axis of rotation of the impeller 120, as shown in FIG. 12A. When the nozzle 130 is swung in the rotational direction of the impeller 120, the flow of water can be converted into a vortex flow in the rotational direction of the impeller 120 before the water enters the impeller 120. When the nozzle 130 is swung in the direction opposite to the rotational direction of the impeller 120, the flow of water can be converted into a vortex flow in the direction opposite to that rotational direction before the water enters the impeller 120. However, also in this embodiment, high-pressure water is still injected from the nozzle 130 to increase the meridional water flow velocity from V to V′, as shown in FIG. 12B.
On the other hand, for example, Patent Literature 2 discloses a refrigerating apparatus 300 as shown in FIG. 13 as another apparatus using a pump device. In this refrigerating apparatus 300, water as a refrigerant is circulated. Specifically, the refrigerating apparatus 300 has a main circuit 310 in which an evaporator 311, a compressor 312, and a condenser 313 are connected in this order. Water is retained in the evaporator 311 and the condenser 313. The compressor 312 draws water vapor from the evaporator 311, compresses the vapor, and discharges the compressed vapor to the condenser 313. The water retained in the evaporator 311 is circulated through a heat absorbing circuit 320 via a loading portion 321. The water retained in the condenser 313 is circulated through a heat dissipating circuit 330 via a cooling tower 331. The heat absorbing circuit 320 and the heat dissipating circuit 330 are each provided with a pump device 200.